Fan shroud exit structure

ABSTRACT

An internal combustion engine, having a heat exchange cooling system, a fan for moving air therethrough and a shroud and shroud exit section for controlling the air path. The shroud exit encloses the fan and includes throat (CF) radial expander (R) and radial flat (RF) sections whereby air is drawn through the heat exchanger axially and expelled radially along said exit sections. The fan has a projected axial width (AW) such that a general relationship exists with the shroud exit sections: CF AW/3, RF AW/3, and R 2AW/3.

States Patent [1 1 Mar. 25, 1975 [73] Assignee: International HarvesterCompany,

Chicago, Ill.

[22] Filed: Apr. 5., 1973 [21] Appl. No.: 348,436

[52] US. Cl 165/1, 123/4149, 165/51, 165/122, 180/54 A, 415/210, 415/219R [51] Int. Cl. F28d 21/00 [58] Field of Search 123/4148, 41.49; 180/54A, 68 R; 415/210, 219 R, D10. 1; 165/1, 51, 122

[56] References Cited UNITED STATES PATENTS 1,519,812 12/1924 Schneider123/4149 X 1,691,598 11/1928 Zbinden 123/4149 1,966,787 7/1934 Buri123/4149 2,142,307 l/1939 De Mey ct a1. 415/210 2,415,621 2/1947 Arnhym415/119 X 2,544,490 3/1951 Curley 415/219 R 2,664,961 l/l954 Goedem.415/210 X 2,668,523 2/1954 Lamb 415/219 R 3,144,859 3/1964 Walton123/4149 FOREIGN PATENTS OR APPLlCATlONS 485,410 10/1953 Italy 123/41497/1939 Australia...l 415/210 107,876 770,848 3/1957 United Kingdom .1123/4149 569,241 1/1933 Germany 1. 415/219 R OTHER PUBLlCATlONSApplications of the Coanda Effect, lmants Reba, Sci entific American,Vol. 214, No. 6, 6-66, pps 8492.

Primary E.raminerAlbert W. Davis, Jr.

Assistant Examiner-S. J. Richter Attorney, Agent, or Firm-Frederick J.Krubel; Floyd B. Harman; John A. Schaerli [57] ABSTRACT An internalcombustion engine, having a heat exchange cooling system, a fan formoving air there through and a shroud and shroud exit section forcontrolling the air path. The shroud exit encloses the fan and includesthroat (CF) radial expander (R) and radial flat (RF) sections wherebyair is drawn through the heat exchanger axially and expelled radiallyalong said exit sections. The fan has a projected axial width (AW) suchthat a general relationship exists with the shroud exit sections: CF=AW/3, RF =AW/3, and R I 2A W/3.

14 Claims, 4 Drawing Figures sum 1 0 2 PATENTEDHARZSHNS mama p 2 F JQL FM LL PRIOR ART FAN SHROUD EXIT STRUCTURE This invention relates to acooling assembly and more particularly to a contoured fan shroud exitsection and a fan located therein.

Most vehicles in general use today are driven by internal combustionengines. These engines being heat producing are for the most part watercooled, that is the engine is jacketed for circulation of water whichtakes up the heat and subsequently transfers it to the atmosphere. Theradiator is used for cooling the liquid circulating through the engineby dissipating the heat to an air stream. The air flowing through theradiator absorbs the heat and carries it out into the atmosphere.Different types of fan systems are used to achieve the necessary airvelocity through the radiator. That is, some fan assemblies draw airfrom the atmosphere through the radiator and back over the enginethereafter exiting to the atmosphere. This type of fan is known as anaxial flow suction fan, drawing air axially through the radiator anddischarging it into the engine compartment. Other fans work in thereversed manner, that is, they draw air from the engine compartmentwherefrom it is blown forwardly through the radiator to achieve thenecessary radiator cooling. This latter system is often employed whenthe vehicle is performing tasks that generate large amounts of dust orair borne particles, to keep such material from settling in the enginecompartment or where thermal and/or air pollution are detrimental tooperator environment. This dust problem is found in many cases to have adetrimental effect upon the engine and its performance while heat andnoise reduce the efficiency of the operator. Baffle systems are ofteninvolved to redirect the air drawn rearwardly by the suction fan,however, such devices are often complicated and as is apparent employadditional parts, labor, and services. The reverse or forwardly blownair through the radiator also suffered from the fact that the air wasoften heated substantially by the passage around the hot engine and,depending'upon how fast the vehicle was moving forwardly necessitatedadditional fan power to overcome the rearward vehicle generated airstream. With the increase in power deliv' ered to the fan, fuelconsumption increased and noise pollution increased.

It is thus apparent that both above methods possess characteristicswhich are far from that which aredesirable. It is therefore an object ofthis invention to provide a cooling assembly which directs dust and airborne particles so as to enhance their expulsion from the enginecompartment. Yet another object of this invention is to provide an airexit section for a fan shroud whereby maximizing air flow and improvingoperator environment by reducing thermal, noise, and air pollution.Still another object of this invention is to provide a fan shroud exitsection and a fan having a relationship whereby optimum air flow andnoise values are achieved. Another. object ofthis invention is toprovide a fan shroud exit section and a fan oriented therein whereby theair flow discharge path can be tailored and, ifso desired, bent to exitradially. A further object of this invention is to provide a fan shroudwith an exit section which is capable of producing the Coanda effect.Still another object of this invention is to provide an air exit sectionand a fan having a relationship whereby the Coanda effect can bemaintained over a substantial range of fan speeds. Still another objectof this invention is to provide an engine cooling assembly which doesnot direct heated air toward the operator station.

In accordance with the preferred embodiment of this invention a vehicleis provided having a liquid cooled internal combustion engine and aradiator cooling sys' tem for dissipating the heat produced. Theradiator cooling system includes a standard radiator, an axial flow fanfacing the radiator and having a plurality of angular blades whereby airis drawn rearwardly through the radiator. A shroud rearwardly extendsfrom the back face of the radiator to channel air through the radiatorand hamper the fan from drawing air which has not passed through or atleast come in contact with the perforated heat exchanging surfaces ofthe radiator. For the most part the shroud encloses the entireperforated heat exchanging rear area of the radiator. A fan shroud exitmeans is also provided having secured to the backwardly extendingportion oftbe fan shroud and extending rearwardly thereof as well asoutwardly. As will be later explained it is the particular contour ofthis exit section in combination with an axial flow fan located therein,the location thereof also being important, which allows the air streamto be converged and directed radially away from the engine compartment.As is apparent this invention is also applicable to a stationary enginewhere it is desired to direct the air stream.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings, in which;

FIG. 1 is a side elevation of an internal combustion engine showing thedevice of my invention attached to a vehicle;

FIG. 2 is a fragmentary vertical section showing the relationship of thefan to the contoured exit section;

FIG. 3 is a top view of a tractor showing the air stream of the priorart fan assemblies; and

FIG. 4 is atop view of a tractor showing the directed air streamachieved with the radiator cooling assembly herein disclosed.

While the invention will be described in connection with a preferredembodiment, it will be understood that it is not intended to limit theinvention to that embodiment. On the contrary, it is intended to coverall alternatives, modifications and equivalents as may be includedwithin the spirit and scope of this invention as defined by the appendedclaims.

Turning first to FIG. 1 there is shown a conventional water cooled heatproducing internal combustion engine means 10 forwardly carried onlongitudinally extending parallel support means 12 of vehicle means 14.As shown herein vehicle means 14 is a tractor, however, as willhereafter become more apparent this invention can be applied to any typeofvehicle employing a heat generating internal combustion engine or anyother portable or stationary device requiring an air moving fan.Forwardly mounted is a water cooling radiator means 16 employed todissipate the engine generated heat. Water flows between the waterjacketon the engine (not shown) and the radiator through a series of fluidcommunicating means l8 and 20. In this particular embodiment sheet metalmeans 22 encircles engine means 10 thereby forming the enginecompartment area means 24.

Carried at the forward end of engine means 10 is a fan shaft means 26whereby power is delivered to drive fan means 28. As is apparent, theparticular mode whereby power is transmitted thereto is not critical andbelts and pulleys could also be employed. As employed here, fan means 28is a rotatable suction fan positioned opposite the radiator means 16,and normally creating a flow of air or drawing in a stream of coolingair rearwardly through the radiator with a subsequent axial dischargethereof. This axial flow of air is directed to the fan means by a shroudmeans 30. The particular shape of the forward section 32 is dependentupon the shape and design of the perforated heat exchanging design ofthe radiator. The nature of the connection between the leading edge of32 and the rear face 34 of the radiator will be dependent upon theparticular characteristics of these components, that is, someconnections being provided with air gaps while others are substantiallysealed over the entire circumference of the enclosure. In the preferredform of this invention the entire perforated area is substantiallysealed against the passage of air from any other direction exceptthrough the radiator. From the forward edges the shroud means (be it ataper transition as shown or a box type) converges rearwardly to acircular rear section 36.

Referring now to FIG. 2 wherein is more clearly shown a shroud exitmeans 38 extending rearwardly and outwardly from shroud edge 36. Theconnection between the shroud and the shroud exit can be achieved by anysuitable means, however, it is desirable that such connection berelatively free of gaps or spaces which would allow the passage of air.Exit shroud means 38 includes a tubular means 40, an arcuated meansportion 42 and a flat flange portion means 44. For the most part tubularmeans portion 40 forms the leading edge of the exit shroud means whilearcuated means portion 42 still extending generally rearwardlysimultaneously extends outwardly around an arch the reference pointofwhich is defined as point 46. That is, arcuated section 42 has ageneral bell-shaped appearance being a section of a transition surfaceor some approximation thereof. In the preferred embodimcnt arcuatcdsection 42 is a section of a constant radius arch. Flat flange portion44 forms the trailing edge of exit shroud means 38 and has a major planeperpendicular to that of tubular section 40. For purposes of simplicity,tubular means 40 will be hereafter referred to as the cylindrical throatmeans, arcuated portion 42 will be referred to as the radial expandingmeans and flat flange portion 44 will be referred to as radial flatmeans. Overall the entire fan shroud exit means 38 has a horn-likeconfiguration.

As previously stated, fan means 28 is rotatingly carried adjacent saidradiator means and operably to establish a flow of cooling airtherethrough. Fan means 28 includes a plurality of fan blade means 48(only one shown) as is well known in the art. As shown in FIG. 2 fanmeans 28 is surrounded by said contoured fan shroud exit section 38. Theenclosure of the fan means 28 within shroud means 30 is such that afront plane struck out by the leading edge 50 is coextensive and passesthrough the leading section of throat means 40 and a rear plane struckout by trailing edge 52 is about coextensive and parallel with saidradial flat portion 44. It should be noted, however, that there is aplus or minus error factor involved in both of these values of about 12percent of AW. That is, the respective planes formed by the blade meanscan be within about 12 percent of optimum and still functionsatisfactorily within 4 the scope of this invention. Thus, within thisrange the direction air stream will still be substantially radial.

It has been determined, however, that best results are obtained when thefront plane struck out by leading edge means 50 passes through thejuncture point between converging shroud 36 and the throat section 40.Even more determinative on the result is the relationship between therear plane struck out by trailing edge means 52 and the radial flatportion 44. Overall performance is achieved when the rear plane and theradial flat portion 44 are coextensive and parallel. Deviations fromthis orientation cause the air stream to change more rapidly thancorresponding percentage changes in the front plane location.

The following relationship exists between these parameters: RF =AW/3, CFAW/3, and R 2AW/3 where RF is the length of the radial flat portion 44,(F is the length of the cylindrical throat section 40 and R is a radiusof the radial expanding section 42 or distance from the reference pointto the transistion surface and AW is the projected axial width of fan28.

Although not obvious from a simple consideration of the layout thecooling assembly embodied herein, horsepower savings and noise reductionare realized. The geometry of the shroud exit and positioning of the fantherein so effects the cooling characteristics of the assembly thatfewer rpms of the fan are necessary to achieve the same temperaturereduction ofthe coolant. Hence, decreasing the fan speed yields areduction of fan generated noise and power required to drive the fan.Because of the radial discharge of the air stream dust and particlematter are swept away from the operator and not back on him. The same istrue for the heat which has been passed to the air, it issues away fromthe operator station.

FIGS. 3 and 4 show the path in which air is dispersed by the fan meanscomprising again a standard assembly and the improved assembly, thus,the achieved is apparent.

In actual tests on an International Harvester tractor model numberFl()26 equipped with the improved cooling assembly provided the samecooling capacity while making a number of improvements. These ineludedabout a 20 percent reduction in fan drive power, about a 6dB reductionin actual fan noise, 4dB reduction of overall vehicle noise at operatorstation and operator station temperature reductions of 20F at his feet,8F at his head and 5F at the steering wheel. It thus is apparent thatshroud exit geometry and fan relationships can make substantialimprovements in the air flow and its discharge direction, noise, andrequired fan drive power characteristics ofa cooling fan. Louver means56 can also be provided to allow the easy and quick dissipation of theradially discharged air.

The amount or relation of the fan means 28 to the exit section means 38is most conveniently expressed in terms of the amount of the fan whichis exposed past the end of the shroud or projects rearwardly thereof. Ithas been found that a X,,-equal to zero gives optimum results; however,reasonable results can be achieved by having X,.; about equal to plus orminus 12 percent of AW. That is, as explained previously when the planeswept out by the rear edge is coextensive with the surface of the radialflat or within the tolerance set forth. By changing the orientation ofthe fan with respect to the fan exit section it is also possible todirect the air stream, straight back, at an angle off radial, etc.,

depending on preference and need.

Thus it is apparent that there has been provided a heat exchange systemincluding, a heat exchange means such as a radiator, a fan shroud and afan shroud exit section with a fan therein. An exit section includes, inorder, a cylindrical throat section, a radial expanding section, and aradial flat portion. The leading edge of the cylindrical throat sectionbeing secured to the shroud around its entire circumference. The fanassembly carried in the shroud exit section includes a plurality of fanblades having front or leading edges and trailing or rear edges. Theseedge means sweep out planes as they rotate, that is, a front and rearplane. The front plane for the most part should intersect thejunctionbetween the shroud end and the cylindrical throat while the rear planeshould be parallel to and coextensive with the radial flat portion. Byexperimentation it has been determined that the relationship of the rearplane to the radial flat is the more critical of the two parameters. [nthe assembly the following relationship plus or minus 12 percent ofAWexists: RF =AW divided by 3, (F AW divided by 3, and R 2AW divided by 3where RF is the length of the radial flat portion, CF is the length ofthe cylindrical throat, R is the distance from the referencepoint to theradial expanding section and A W is the projected axial width of thefan. As has been pointed out previously the R value in the preferredembodiment is the radius of the radial expanding section, that is, theradial expanding section is a part of a circle. However, as is apparentit may deviate from this preferred form. Accordingly, the fan inducedstream of air is converged and directed out of the shroud exit parallelto the radial flat portion thus avoiding the passage of dust andparticle laden air currents against the engine and subsequently againstthe operator station.

Thus it is apparent that there has been provided, in accordance with theinvention, a shroud exit means that fully satisfies the objects, aims,and advantages set forth above. While the invention has been describedin conjunction with specific embodiments thereof, it is evident thatmany alternatives, modifications, and variations will be apparent tothose skilled in the art in light ofthe foregoing description.Accordingly, it is intended to embrace all such alternatives,modifications, and variations as fall within the spirit and broad scopeof the appended claims.

What is claimed is:

l. A method of transferring internal combustion en- 'gine produced heatfor cooling said engine comprising the steps of:

transferring the engine generated heat to a coolant;

passing said heated coolant through a heat exchange means;

generating an air stream with a fan means;

drawing the air stream through the heat exchanger transferring heatthereto;

guiding the heated air stream from said heat exchanger to said fan witha shroud; and

expelling the heated air stream from the fan means over a contoured fanshroud configured to produce a Coanda effect directing the air streamgenerally radially outward, said fan shroud being positioned generallyaround said fan.

2. A method for dissipating internal combustion en gine produced heatcomprising the steps of:

6 absorbing said heat in a liquid media; transporting heated liquidmedia to a heat exchanger means;

circulating said heated liquid media through said heat 5 exchanger;

generating an airstream with a fan means;

drawing the air stream through said heat exchanger to effect heattransfer thereb'etween and expelling the heated air from the fan meansovera fan shroud configured to produce a Coanda effect directing the airstream generally radially outward, said fan shroud being positionedgenerally around said fan.

3. A method of moving air to dissipate the heat generated by a liquidcooled internal combustion engine such that a Coanda effect is achievedcomprising the steps of:

passing liquid from said internal combustion engine through a heatexchanger means;

generating an air stream with a fan means;

drawing the air stream through the heat exchanger;

guiding the air stream from the heat exchanger to the fan means; andexpelling the air stream from the fan over a contoured fan shroudconfigured to produce a Coanda effect directing the air stream generallyradially outward, said fan shroud generally surrounding said fan. 4. Amethod of handling air for cooling a water jacketed internal combustionengine such that a Coanda effeet is achieved comprising the steps of:

generating an air stream with a fan means; drawing the air streamthrough a heat exchanger; guiding the air stream from said heatexchanger with a shroud means; and

expelling the air stream over a contoured fan shroud means configured toproduce a Coanda effect directing said air stream generally radiallyoutward.

5. A heat transfer system for an internal combustion engine comprising:

a heat exchanger including a front and a rear section:

a shroud having a forward section arranged to enclose said rear sectionof said heat exchanger, and a rearwardly extending unitary contouredexit sec tion including a cylindrical throat, radial expanding sectionand a radial flat portion; a'fan assembly including a plurality of fanblades having leading and trailing edges, said leading edges positionedadjacent said heat exchanger wherein the following relationship withinplus or minus 12 percent ofAWexists: RF =AW/3, CF =AW/3, and R 2A W/3where RF is the length of the radial flat portion, CF is the length ofthe cylindrical throat, R is the radius of the radial expanding sectionand AW is the projected axial width of the fan means whereby fangenerated noise and horsepower requirements of said engine are reduced.

6. The heat transfer system of claim 5 wherein the trailing edge of saidfan forms a plane parallel, plus or minus 12 percent, with said radialflat portion, whereby the fan induced stream ofair is converged anddirected out parallel to the radial flat portion.

7. A heat transfer system for an internal combustion engine comprising:

a heat exchanger having a front and a rear section;

a shroud having a forward section arranged to enclose said rear section,and a rearwardly extending unitary contoured exit section includingmeans defining a cylindrical throat, means defining a radial expandingsection and a radial flat portion; I

a fan assembly including a plurality of fan blades each having a leadingand a trailing edge, said leading edge being positioned adjacent saidheat exchanger, wherein the following relationship exists: RF =AW/3, CF=AW/3, and R =2 A W/3 where RF is the length of the radial flat portion,CF is the length of the cylindrical throat, R is the radius of theradial expanding section and AW is the projected axial width of the fanwhereby fan generated noise and horsepower requirements are reduced.

8. A cooling system for an internal combustion engine comprising:

a radiator including means defining a tube and means defining a rearwardarea; I

a shroud having a forward section arranged to include said rearward areaof said radiator, and means defining a rearwardly extending unitarycontoured exit section including a cylindrical throat, a radialexpanding section and a radial flat portion;

a fan assembly including a plurality of fan blades each having leadingand trailing edges, said leading edges being positioned adjacent saidradiator, wherein the following relationship plus or minus 12 percentexists: RF =AW/3, CF =AW/3 and R 2 A W/3 where RF is the length of theradial flat portion, (F is the length ofthe cylindrical throat, R is theradius of the radial expanding section and AW is the projected axialwidth of the fan whereby the fan induced stream of air is converged anddirected out generally parallel to the radial flat portion.

9. The cooling system of claim 8 wherein:

said radiator includes means defining a rearwardly extending perforatedarea;

said shroud enclosing said perforated area, and

said trailing edges of said fan blades are coextensive plus or minus 12percent with said radial flat portion wherein the following relationshipexists: RF AW/3, CF =AW/3, and R 2AW/3 wherev CF is the length of thecylindrical throat, R is the radius of the radial expanding section andAW is the projected axial width of the fan.

10. A vehicle having an operator station, an internal combustion engine,a radiator for cooling fluid from said engine an axial flow fan axiallyfacing said radiator and including a plurality of angular blades drawingair rearwardly through said radiator, and a shroud rearwardly extendingfrom said radiator wherein the improvement comprises:

a unitary shroud exit section closely surrounding said fan and extendingin the same direction as said shroud including a tubular portion formingthe leading edge thereof, an arcuate portion extending generallyrearwardly and outwardly from said tubular portion and terminating in aflat flange portion forming the trailing edge of said shroud and lyingin a plane perpendicular to said tubular portion, said fan disposedwithin at least a portion of said shroud exit section wherein thefollowing relationship plus or minus 12 percent exists: RF=A W/3, CF=AW/3 and R=2 AW/3 where RF is the length of the flat flange portion, CFis the length ofthe tubular portion, R is the radius of the arcuateportion and A W is the projected axial width of the fan whereby fangenerated noise and horsepower requirement of said engine are reduced.

11. The shroud exit section of claim 10 wherein said fan has a frontplane which intersects said tubular portion and a rear plane whichintersects, plus or minus 12 percent, said flat flange portion whereby astream of air is converged and directed outwardly parallel to said flatflange portion to prevent the passage of dust and particle laden airagainst said engine, and engine heat against said operator station.

12. The shroud exit section of claim 11 wherein said tubular portion issecured to said shroud around the entire circumference thereof forming ajunction section; and

said front plane struck out by said fan intersects said junctionsection.

13. A vehicle having an operator station and an internal combustionengine, a radiator for cooling fluid from said engine, an axial flow fanaxially facing said radiator and including a plurality of angular bladesdrawing air rearwardly through said radiator, and a shroud rearwardlyextending from said radiator wherein the im provementcomprises:

a unitary fan shroud exit portion secured to said shroud and extendingrearwardly thereof including:

a cylindrical throat defining a leading edge, a midially expandingportion, and a radial flat portion defining a trailing edge; said fanbeing enclosed therein, said blade means defining a front planecoextensive with said leading edge wherein the following relationshipexists: RF =A W/3, CF A W/3, and R =2 AW/3 where RF is the radial flatportion, CF is the cylindrical throat, R is the radius of the radialexpanding section and AW is the projected axial width of the fan wherebyfan generated noise and horsepower requirements ofsaid internalcombustion engine are reduced.

14. The improvement of claim 13 wherein:

said fan shroud exit portion is secured to said shroud around its entirecircumference; and

said blade means defines a rear plane, said plane being coextensive withsaid radial flat means plus or minus 12 percent.

1. A method of transferring internal combustion engine produced heat forcooling said engine comprising the steps of: transferring the enginegenerated heat to a coolant; passing said heated coolant through a heatexchange means; generating an air stream with a fan means; drawing theair stream through the heat exchanger transferring heat thereto; guidingthe heated air stream from said heat exchanger to said fan with ashroud; and expelling the heated air stream from the fan means over acontoured fan shroud configured to produce a Coanda effect directing theair stream generally radially outward, said fan shroud being positionedgenerally around said fan.
 2. A method for dissipating internalcombustion engine produced heat comprising the steps of: absorbing saidheat in a liquid media; transporting heated liquid media to a heatexchanger means; circulating said heated liquid media through said heatexchanger; generating an air stream with a fan means; drawing the airstream through said heat exchanger to effect heat transfer therebetweenand expelling the heated air from the fan means over a fan shroudconfigured to produce a Coanda effect directing the air stream generallyradially outward, said fan shroud being positioned generally around saidfan.
 3. A method of moving air to dissipate the heat generated by aliquid cooled internal combustion engine such that a Coanda effect isachieved comprising the steps of: passing liquid from said internalcombustion engine through a heat exchanger means; generating an airstream with a fan means; drawing the air stream through the heatexchanger; guiding the air stream from the heat exchanger to the fanmeans; and expelling the air stream from the fan over a contoured fanshroud configured to produce a Coanda effect directing The air streamgenerally radially outward, said fan shroud generally surrounding saidfan.
 4. A method of handling air for cooling a water jacketed internalcombustion engine such that a Coanda effect is achieved comprising thesteps of: generating an air stream with a fan means; drawing the airstream through a heat exchanger; guiding the air stream from said heatexchanger with a shroud means; and expelling the air stream over acontoured fan shroud means configured to produce a Coanda effectdirecting said air stream generally radially outward.
 5. A heat transfersystem for an internal combustion engine comprising: a heat exchangerincluding a front and a rear section; a shroud having a forward sectionarranged to enclose said rear section of said heat exchanger, and arearwardly extending unitary contoured exit section including acylindrical throat, radial expanding section and a radial flat portion;a fan assembly including a plurality of fan blades having leading andtrailing edges, said leading edges positioned adjacent said heatexchanger wherein the following relationship within plus or minus 12percent of AW exists: RF AW/3, CF AW/3, and R 2AW/3 where RF is thelength of the radial flat portion, CF is the length of the cylindricalthroat, R is the radius of the radial expanding section and AW is theprojected axial width of the fan means whereby fan generated noise andhorsepower requirements of said engine are reduced.
 6. The heat transfersystem of claim 5 wherein the trailing edge of said fan forms a planeparallel, plus or minus 12 percent, with said radial flat portion,whereby the fan induced stream of air is converged and directed outparallel to the radial flat portion.
 7. A heat transfer system for aninternal combustion engine comprising: a heat exchanger having a frontand a rear section; a shroud having a forward section arranged toenclose said rear section, and a rearwardly extending unitary contouredexit section including means defining a cylindrical throat, meansdefining a radial expanding section and a radial flat portion; a fanassembly including a plurality of fan blades each having a leading and atrailing edge, said leading edge being positioned adjacent said heatexchanger, wherein the following relationship exists: RF AW/3, CF AW/3,and R 2 AW/3 where RF is the length of the radial flat portion, CF isthe length of the cylindrical throat, R is the radius of the radialexpanding section and AW is the projected axial width of the fan wherebyfan generated noise and horsepower requirements are reduced.
 8. Acooling system for an internal combustion engine comprising: a radiatorincluding means defining a tube and means defining a rearward area; ashroud having a forward section arranged to include said rearward areaof said radiator, and means defining a rearwardly extending unitarycontoured exit section including a cylindrical throat, a radialexpanding section and a radial flat portion; a fan assembly including aplurality of fan blades each having leading and trailing edges, saidleading edges being positioned adjacent said radiator, wherein thefollowing relationship plus or minus 12 percent exists: RF AW/3, CF AW/3and R 2 AW/3 where RF is the length of the radial flat portion, CF isthe length of the cylindrical throat, R is the radius of the radialexpanding section and AW is the projected axial width of the fan wherebythe fan induced stream of air is converged and directed out generallyparallel to the radial flat portion.
 9. The cooling system of claim 8wherein: said radiator includes means defining a rearwardly extendingperforated area; said shroud enclosinG said perforated area, and saidtrailing edges of said fan blades are coextensive plus or minus 12percent with said radial flat portion wherein the following relationshipexists: RF AW/3, CF AW/3, and R 2AW/3 where CF is the length of thecylindrical throat, R is the radius of the radial expanding section andAW is the projected axial width of the fan.
 10. A vehicle having anoperator station, an internal combustion engine, a radiator for coolingfluid from said engine an axial flow fan axially facing said radiatorand including a plurality of angular blades drawing air rearwardlythrough said radiator, and a shroud rearwardly extending from saidradiator wherein the improvement comprises: a unitary shroud exitsection closely surrounding said fan and extending in the same directionas said shroud including a tubular portion forming the leading edgethereof, an arcuate portion extending generally rearwardly and outwardlyfrom said tubular portion and terminating in a flat flange portionforming the trailing edge of said shroud and lying in a planeperpendicular to said tubular portion, said fan disposed within at leasta portion of said shroud exit section wherein the following relationshipplus or minus 12 percent exists: RF AW/3, CF AW/3 and R 2 AW/3 where RFis the length of the flat flange portion, CF is the length of thetubular portion, R is the radius of the arcuate portion and AW is theprojected axial width of the fan whereby fan generated noise andhorsepower requirement of said engine are reduced.
 11. The shroud exitsection of claim 10 wherein said fan has a front plane which intersectssaid tubular portion and a rear plane which intersects, plus or minus 12percent, said flat flange portion whereby a stream of air is convergedand directed outwardly parallel to said flat flange portion to preventthe passage of dust and particle laden air against said engine, andengine heat against said operator station.
 12. The shroud exit sectionof claim 11 wherein said tubular portion is secured to said shroudaround the entire circumference thereof forming a junction section; andsaid front plane struck out by said fan intersects said junctionsection.
 13. A vehicle having an operator station and an internalcombustion engine, a radiator for cooling fluid from said engine, anaxial flow fan axially facing said radiator and including a plurality ofangular blades drawing air rearwardly through said radiator, and ashroud rearwardly extending from said radiator wherein the improvementcomprises: a unitary fan shroud exit portion secured to said shroud andextending rearwardly thereof including; a cylindrical throat defining aleading edge, a radially expanding portion, and a radial flat portiondefining a trailing edge; said fan being enclosed therein, said blademeans defining a front plane coextensive with said leading edge whereinthe following relationship exists: RF AW/3, CF AW/3, and R 2 AW/3 whereRF is the radial flat portion, CF is the cylindrical throat, R is theradius of the radial expanding section and AW is the projected axialwidth of the fan whereby fan generated noise and horsepower requirementsof said internal combustion engine are reduced.
 14. The improvement ofclaim 13 wherein: said fan shroud exit portion is secured to said shroudaround its entire circumference; and said blade means defines a rearplane, said plane being coextensive with said radial flat means plus orminus 12 percent.